1. Field of the Invention
Neospora caninum is a protozoan parasite that is the causal agent of bovine neosporosis; infection results in high levels of abortion and stillbirth in cattle. This invention relates to a vaccine which comprises a recombinant Neospora cyclophilin protein (rNcCyP) and the method of using rNcCyP as a vaccine to protect cattle from N. caninum infection.
2. Description of the Relevant Art
N. caninum is a protozoan parasite that causes neosporosis in dogs and cattle (Dubey et al. 1989. J. Parasitol. 75: 146-148; Dubey et al. 2007. Clin. Microbiol. Rev. 20: 323-367). The only recognizable clinical manifestations of neosporosis in cows are reproductive failure such as abortion and still birth and birth of congenitally infected and clinically weak calves (Dubey, J. P. 2007. Vet. Clin. North Am. Food Anim. Pract 21: 473-483).
A killed whole-cell N. caninum tachyzoite vaccine has been tested (1) in cattle (Andrianarivo et al. 2005. Parasitol. Res. 96: 24-31; Andrianarivo et al. 2001. Parasitol. Res. 87: 817-825; Andrianarivo et al. 1999. Int. J. Parasitol. 29: 1613-1625; Andrianarivo et al. 2000. Int. J. Parasitol. 30: 985-990; Barling et al. 2003. J. Am. Vet Med. Assoc. 222: 624-627; Choromanski and Block. 2000. Parasitol. Res. 86: 851-853; Moore et al. 2005. Vet Parasitol. 130: 29-39; Romero et al. 2004. Vet. Parasitol. 123: 149-159; Williams et al. 2007. Infect. Immun. 75:1342-1348), (2) in mice (Liddell et al. 1999a. J. Parasitol. 85: 1072-1075; Miller et al. 2005. Int. J. Parasitol. 35: 821-828) and (3) in sheep (Jenkins et al. 2004b. Am. J. Vet Res. 65: 1404-1408; O'Handley et al. 2003. Am. J. Vet. Res. 64: 449-452); this vaccine could only achieve partial protection and was inconsistent from study to study. The currently marketed vaccine (NeoGuard) against bovine neosporosis using the whole-cell N. caninum tachyzoite lysate (NcAg) as antigen had a reported protection rate of approximately 50% in beef cattle (Romero et al., supra). The approach of live attenuated N. caninum tachyzoite vaccine was also attempted in mice and cattle (Lindsay et a. 1999. J. Parasitol. 85: 64-67; Miller et al., supra; Ramamoorthy et al. 2007a. Int J. Parasitol. 37: 1521-1529; Ritter et al. 2002. J. Parasitol. 88: 271-280), but its efficacies need to be further confirmed. Williams and colleagues have recently demonstrated that cows immunized with Nc Nowra, an N. caninum isolate that is low in virulence, were protected against fetal deaths. The whole-cell tachyzoite lysate had no effect in the Williams study and is thus a further indication that the approach of whole-cell tachyzoite lysate vaccine appears not to work (Williams et al., supra).
Concurrent with research relying on the use of whole-cell Neospora tachyzoite antigen, subunit vaccine research has revealed that single or multivalent subunit vaccines can result in equally effective or better protection than whole cell or lysate vaccines. In addition, they elicit specific immune responses. The subunit vaccine candidates tested so far included NcSRS2 in dogs and mice (Cannas et al. 2003a. Parasitology 126: 303-312; Cho et al. 2005. Korean J. Parasitol. 43: 19-25; Haldorson et al. 2005. Int. J. Parasitol. 35: 1407-1415; Nishikawa et al. 2000. Int. J. Parasitol. 30: 1167-1171; Nishikawa et al. 2000. Parasitol. Res. 86: 934-939; Nishikawa et al. 2001a. J. Clin. Microbiol. 39: 3987-3991; Nishikawa et al. 2001b. Vaccine 19: 1710-1716; Pinitkiatisakul et al. 2007. Vaccine 25: 3658-3668; Pinitkiatisakul et al. 2005. Vet Parasitol. 129: 25-34; Ramamoorthy et al. 2007b. Int. J. Parasitol. 37: 1531-1538; Vemulapalli et al. 2007. Vet. Parasitol. 148: 219-230), NcSAG1 (Cannas etal., 2003a, supra; Nishikawa et al. 2001c. Vaccine 19: 1381-1390; Nishikawa et al. 2001b, supra), NcMIC3 (Cannas et al., 2003b. J. Parasitol. 89: 44-50; Ramamoorthy et al. 2007a, b, supra), NcGRA7 (Jenkins et al. 2004a. Infect. Immun. 72: 1817-1819; Liddell et al. 2003. J. Parasitol. 89: 496-500; Vemulapalli et al., supra), NcsHSP33 (Liddell et al. 2003, supra), NcDG1 and NcDG2 (Cho et al., supra), NcMIC1 (Alaeddine et al. 2005. J. Parasitol. 91: 657-665; Ramamoorthy et al. 2007a, b, supra), NcAMA1 (Zhang et al. 2007a. Mol. Biochem. Parasitol. 151: 205-212), NcP0 (Zhang et al. 2007b. Mol. Biochem. Parasitol. 153: 141-148), and NcGAR2, NcGRA6 (Ramamoorthy et al. 2007a, b, supra). Of all the vaccine candidates tested so far, the most efficacious and promising subunit vaccines include those that use NcSRS2 or NcGRA7 as antigen.
Thus, although numerous studies have been attempted to develop an efficacious vaccine against bovine neosporosis, to date there are no effective chemo- or immuno-prophylactic treatments for this protozoal disease. Recent analysis of the published quantitative data indicated that vaccination might be the most economical intervention in the control of neosporosis, particularly in herds with high prevalence of N. caninum infection (Reichel et al. 2006. Vet Parasitol. 142: 23-34). This further illustrates the urgent need to develop a vaccine against neosporosis in cattle which would prevent or limit the disease.